I'm fairly certain (and George Upstairs has confirmed so) that this is off the ECT Leyland PD3/6 Alexanders double deck 655 (ASC 655B) bus that came a cropper at Oxgangs on Wednesday June 18 1975 when it fell over one day and was subsequently scrapped. I have memories of finding the hulk in Shrubhill Works and managing to acquire this. Mind you someone with a fleet body list for Edinburgh should be able to verify it. The serial number is E/1/3463/5. Alexanders were for many years in the 1960s to the 1980s the coach-builder of choice for Edinburgh-based up the road in Falkirk they are of course, still in business.
As for the accident I have the Edinburgh Evening News for the day-and nine were hurt in the accident-a lorry hit the bus as it turned right from Oxgangs Road North and Oxgangs Avenue.
From George Upstairs: So you're right Mike. Also, see the beast itself.